There are 48 Enforcer Events to get Gold on. This will take about 10 hours and some retrying of events to place first. Try to stay behind a racer to slipstream and practice drifting to help build up your nitrous. Keep practicing and most of the events should not be too much of a problem except for some really tricky ones that should come if you just keep at it.
Some tips are:
Learn when to boost. Going up hills and long straight aways will be perfect times to use your precious nitrous.
Explore the shortcuts. Some shortcuts will help you a whole lot and others will mess you up even more. If you are having trouble with an event, find out which route benefits you the best.
Drift. This is one of the better ways to get your nitrous refilled and will help you from hitting walls on those sharp turns.
Do not waste power ups. These will help you during Interceptor events and Hot Pursuits. Start the events trying to use brute force to take out your opponents. When you are getting low on time or have a lot of racers about to be knocked out, use your equipment and take them out.
You can restart the event if you mess up to bad so you do not have to watch too many loading screens. On the downside, you do not get any bounty if you do this. So if you are getting 2nd or 3rd place, the bounty you earn can help you rank up for the rank achievements.